考试用时存入秒数，最后用方法转换一成这种格式 （00：00：00）

//考试用时
        $times = 60;//秒数
        $result = '00:00:00';
        if ($times>0) {
                $hour = floor($times/3600);  
                $minute = floor(($times-3600 * $hour)/60);  
                $second = floor((($times-3600 * $hour) - 60 * $minute) % 60);  
                $result = $hour.':'.$minute.':'.$second;
        }  

        $this->yongshi = $result;//考试用时